Method of forming hybrid metal ceramic components

ABSTRACT

A monolithic composite turbine component includes at least one first region of a first material and one second region of a second material formed by solid freeform fabrication (SFF). The first material may be a metal and the second material may be a ceramic or a ceramic matrix composite. Transition regions between the metal region and ceramic region are functionally graded regions to minimize internal stress during temperature fluctuations.

FIELD OF THE INVENTION

This invention relates to turbine engine components.

BACKGROUND

In the pursuit of ever higher efficiencies, gas turbine manufacturershave long relied on continually increasing turbine inlet temperatures toprovide boosts to overall engine performance. In typical modern engineapplications, the gas path temperatures within the turbine exceed themelting point of some component materials. As a result, dedicatedcooling air extracted from the compressor is used to cool the gas pathcomponents in the engine incurring significant cycle penaltiesespecially when cooling is utilized in the low pressure turbine(sometimes also referred to as the power turbine).

To reduce these cycle penalties, much research has gone intoimplementing high temperature materials into the construction of thesecomponents. A popular area of research material is the development ofceramic matrix composites (CMC's). Turbine applicable CMC's aretypically composed of silicon-carbon fibers in silicon or boron dopedsilicon infiltration matrices. These CMC's are laid up in alternatingplies whose orientation is tailored to the intended direction of maximumtensile loads. Other materials of use are monolithic ceramics made of,for example, silicon or silicon compounds. While having significantlyhigher temperature capabilities, strengths compared to metallic partsare orders of magnitude lower limiting the capability of these materialsin implementation. Further, silicon based components are susceptible towater degradation, and exhibit silicon migration into the surroundingmetallic parts that they may come in contact with at elevatedtemperatures.

Ceramics offer benefits of higher temperature capability and lowercooling requirements which correlate to improved efficiency and reducedemissions. One of the main challenges of implementing ceramics for highpressure turbine application, is their low thermal shock resistance andlow overall strength. In an effort to overcome these limitations,development of numerous structural hybrid designs and joining techniqueshave been made available that combine metal and ceramic elements thatminimize thermal stresses and thermal expansion rates. These mechanicalinterfaces, however, have been shown to be unreliable for implementationinto highly stressed applications, such as a turbine blade or vane. Theinterfaces must be specially coated for contact with metallic parts dueto abrasive wear and silicon migration. Further, mechanical interfacesnecessitate a sealing mechanism which incurs a cooling leakage penaltythat increases the need to flow cooling air into the part.

Stress free ceramic to metal joins in these components would offerimproved performance.

SUMMARY

A monolithic composite turbine component includes at least one region ofa first material attached to a second region of a second material bysolid freeform fabrication (SFF). The first region is preferably metaland the second region is preferably ceramic or ceramic matrix composite.The transition regions between the first and second regions arefunctionally graded to minimize internal stress during operation.

In an embodiment, a method of forming a monolithic composite turbinecomponent includes forming a first region attached to a second region bysolid freeform fabrication (SFF) additive manufacturing. The transitionregions between the first and second regions are functionally graded tominimize internal stress during operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a two component powder bedadditive manufacturing process.

FIG. 2 is a perspective view of a monolithic composite turbine nozzlewith functionally graded material transitions.

FIG. 3 is a schematic representation of a two component selective lasermelting powder deposition additive manufacturing process.

FIG. 4 is a schematic representation of a monolithic composite componentof the invention.

DETAILED DESCRIPTION

The thermodynamic efficiency of a gas turbine engine scales directly asthe absolute temperature difference between the inlet and the exhausttemperatures of the working fluid in the gas path of the engine. Thedrive to use materials with increased temperature capability iscontinually hindered by the intrinsic structural properties of turbinematerials at elevated temperatures. This difficulty is being addressedby the use of composite materials with widely differing thermalmechanical response properties. Ceramics exhibit high temperatureresistance to deformation, but low resistance to fracture even at hightemperatures. Metals, in contrast, exhibit high resistance todeformation and fracture, but are limited to applications in thevicinity of their melting temperatures. Combinations of metal andceramic structures in composite materials such as ceramic matrixcomposites (CMC's) wherein the filler (metal or ceramic) is a fiber orotherwise elongated form of material and the matrix is a ceramic formedby, for instance, molten or gaseous infiltration, can exhibit both hightemperature fracture resistance due to fiber reinforcement andenvironmental degradation due to erosion.

Situations exist, however, in engine design wherein the beneficial andcontrasting, properties of ceramics, metals and CMC's are all requiredin a single composite component. In this case, the joints betweenseparate parts of a component may be a weak link due to thermal andthermal mechanical property disparities across each joint in a cyclicthermal gradient. Thermal expansion discontinuities across, forinstance, a metal and ceramic or CMC interface may result in measureablestress concentrations leading to environmental degradation at the jointand possible failure.

With the advent of solid freeform fabrication (SFF) technology using,for instance, additive manufacturing techniques, turbine componentsexposed to varying severe environments in a hot gas path can be formedwherein different materials can be used with positive results in areasof a part exposed to different environments.

Solid freeform fabrication is a process wherein three-dimensional (3D)objects are produced by a layer by layer technique or the deposition ofindividual solid, liquid or semi-solid portions of a material onspecific regions of an object according to a digital model of the objectstored in the memory of a computer controlled deposition apparatus.Common energy sources used in SFF are laser and electron beams. Metals,ceramics, and polymers can be used as build materials. Direct SFFfabrication of useful components are now known in the art.

Powder based layer by layer additive SFF manufacturing processessuitable for the present invention include selective laser sintering(SLS), direct laser sintering (DLS), selective laser melting (SLM),direct laser melting (DLM) and others known in the art. A preferredtechnique for the present invention is direct laser melting.

Powder based direct material deposition SFF manufacturing processesinclude direct laser melting (DLM), direct laser deposition (DMD), laserengineered net shaping (LENS), shape deposit manufacturing (SDM),directed light fabrication (DLF), three dimensional cladding and othersknown in the art. A preferred technique for the present invention isdirect laser melting.

An embodiment of the present invention is the fabrication of amonolithic composite turbine component containing regions of at leasttwo different materials, preferably ceramic and metal by solid freeformfabrication (SFF). This embodiment requires at a minimum, at least twopowder sources. A layer by layer fabrication embodiment of the inventionis shown in FIG. 1. Powder bed SFF additive manufacturing process 10includes manufacturing chamber 12 containing devices that produce twocomponent SFF objects by powder bed additive manufacturing. An exampleof process 10 is selective laser melting (SLM). SFF SLM process 10includes powder storage chambers 14 and 16. In a preferred embodiment,storage chamber 14 contains metal powder 24 and storage chamber 16contains ceramic powder 26. SFF SLM process 10 further includes buildchamber 18, laser 20, scanning mirror 22, piston 28 in storage chamber14, piston 30 in build chamber 18 and piston 32 in storage chamber 16.

During operation of SFF SLM process 10, metal powder 24 is fed upward bypiston 28 and spread over build platform 30 by roller 34. After powder24 is spread on build platform 30 by roller 34, roller 34 retracts toposition 42 shown in phantom lines and laser 20 and scanning mirror 22are activated by a control system (not shown) to melt selective areas ofsurface S of powder 24 in build chamber 18 according to a computer modelof solid free form object 36 to form a single solidified layer of SFFobject 36.

In the next step, piston 28 advances to expose another layer of metalpowder 24 in chamber 14 and piston 30 recedes in build chamber 18 toaccept another layer of powder. Roller 34 then advances to spreadanother layer of powder 24 on build chamber 18 and then retracts toposition 42 while laser 20 and scanning mirror 22 are activated to fusea selected area of surface S to form another layer of SFF object 36. Theprocess continues until, for instance, feature 38 is formed from metalpowder 24.

In an embodiment, if, at this point, it is desired to form ceramiccomponent 44 on metal feature 38, from ceramic powder 26 in storagechamber 16, the process changes. Roller 34 advances to position 44,shown in phantom lines. Piston 32, indexes up one layer thickness toexpose ceramic powder 26 to roller 34. Build platform 30 indexes downone layer thickness and roller 34 proceeds to spread one layer ofceramic powder 26 on build chamber 18 creating new ceramic surface S.Roller 34 then retracts to position 44. Laser 20 and scanning mirror 22are activated to fuse selected areas of ceramic powder 26 at surface S.Piston 32 indexes upward one layer of thickness and build platformindexes downward one layer thickness. Roller 34 then spreads anotherlayer of ceramic powder 26 on the solidified surface of ceramic powder26. Laser 20 and scanning mirror 22 are then activated to fuse selectedareas of ceramic powder 26 at surface S according to a computer modeland control system (not shown) of SLM process 10 to form subcomponent 40of component 36.

If another subcomponent, such as metal subcomponent 42 is to be added tocomponent 36 on subcomponent 40, the process is changed to a processforming metal addition 42 attached to subcomponent 40, that is similarto the process forming metal subcomponent 38 as discussed above.

In an embodiment, SFF component 36 may be a turbine nozzle comprisingceramic vane 40 attached to metal platforms 38 and 42. Platforms 38 and42 may be formed of nickel base, iron base or cobalt base superalloys,titanium or titanium alloys. Vane 40 may be formed of a ceramic,silicon, silicon compound or a CMC. The ceramic may be silicon carbide,silicon nitride, silicon oxynitride, aluminum oxide and others known inthe art. A CMC may be C/SiC, SiC/SiC, SiC/C, or mixtures thereof.

In an embodiment, SFF component 36 may be a rotating airfoil, bucket orblade. In another embodiment, SFF component 36 may be a combustor panel,combustor heat shield or combustor fuel nozzle.

As schematically shown in FIG. 1, interfaces 44 and 46 represent sharptransitions in monolithic composite component 36 from metal to ceramicinterface 44, and ceramic to metal interface 46. If transition regions44 and 46 are one layer thick, differences in coefficient of thermalexpansion (CTE) across such a thin interface will cause failure of theinterfaces in severe or even moderate thermal cycling during operation.It is the purpose of this invention to increase the structural integrityof interfaces such as those represented by metal to ceramic interfaces44, and 46 in composite metal ceramic turbine components by formingfunctionally graded transition regions at the interfaces.

Functionally graded materials are a class of materials in which thematerial properties of a component vary with position throughout thecomponent in a predetermined manner usually to minimize designconstraints put on the component. In the example of a turbine nozzleillustrated schematically as component 36 in FIG. 1, it is advantageousto decrease the severity of the coefficient thermal expansion (CTE)mismatch across metal to ceramic interfaces 44 and 46. This may beachieved by creating functionally graded interface regions at interfaces44 and 46 during the SFF formation of component 36.

In an embodiment, the functionally graded regions may be regions inwhich the compositions change from, for instance, 100 percent ceramic to100 percent metal across a certain distance usually in a stepwise orcontinuous manner. According to the rule of mixtures the property P(X)of a composite material composed of a mixture of two types of materialssuch as, A and B with properties P_(A) and P_(B) and volume fractionsV_(A) and V_(B) at a position X across a graded interface is:P_(TOTAL)(X)=P_(A)V_(A)(X)+P_(B)V_(B)(X)

As the transition region expands in size, the severity of mismatchdecreases accordingly. Research suggests that a smooth transition in CTEacross functionally graded zones 44 and 46 of the present inventionrequires at least 20 layers with each layer thickness ranging from 100to 1000 microns to guarantee structural integrity under serviceconditions. Each intermediate zone or layer may have its own geometricalconfiguration defined in the build file and in the control systemdefining the specific mixture of metal to ceramic ratio. For example,the compositional transition of a functionally graded interface betweena metal platform and a turbine vane of the invention may be:

 0-30% span 100% platform metal 30-31% span  90% platform metal 10%ceramic 31-32% span  50% platform metal 50% ceramic 32-34% span  25%platform metal 75% ceramic 35-100% span  100% ceramic

Densification of each layer depends on the materials, laser power,scanning speed preheating temperatures and other input parametersnecessary for consolidation. For instance, ceramic fusing issues mayrequire sintering aids that would reduce the input power density forfusion for the composite powder

A perspective view of schematic monolithic composite metal ceramicturbine nozzle 36 of the invention shown in FIG. 1, with functionallygraded material transitions is shown in FIG. 2 wherein like componentsare numbered accordingly. Nozzle 36 comprises metal platforms 38 and 42,ceramic vanes 40 and functionally graded transitions 45 and 47 replacingabrupt transitions 44 and 46.

An alternate method of producing SFF monolithic composite turbinecomponents with functionally graded zones and interfaces is by powderbased direct material deposition. Direct material deposition offers anadditional degree of freedom over layer by layer SFF processes in thatall three spacial dimensions (x,y,z) can be addressed simultaneouslyduring a build. In direct material deposition, small amounts of materialin solid, semi-molten or molten form are individually deposited to a SFFbody according to a CAD model stored in memory in a direct materialdeposition system. Examples are laser engineered net shaping (LENS),shape deposit manufacturing (SDM), directed light manufacturing (DLF),direct laser melting (DLM), laser based additive manufacturing (LBAM),and others known in the art. A preferred technique for the presentinvention is direct laser melting.

Since an inert atmosphere is not generally required in some directmaterial deposition systems because of the direct material deliveryprocess, larger parts may be produced and higher dimensional depositionpaths and build structures may be achieved.

A schematic of SFF DLM direct material deposition process 50 is shown inFIG. 3. Process 50 includes manufacturing chamber 52, first powder 54,second powder 56, build platform 58, laser 60, scanning mirror 62, SFFdeposited build structure 64 and molten region 66. During SFF directmaterial deposition process 50, first powder 54 is deposited at acontrolled rate onto build platform 58 toward region 66 as indicated byarrows a. Second powder 56 is also deposited at a controlled rate ontobuild platform 58 toward region 66 as indicated by arrows b. Althoughtwo powder sources are indicated in FIG. 3, other powder sources may beemployed. Material deposition in SFF direct material deposition process50 is preferably coaxial with laser 60.

Laser 60 is activated according to a process schedule in a controlsystem (not shown), of process 50 to fuse powders 54 and 56 in region 66on solidified SFF structure 64. Solidification of direct depositedregion 66 results in controlled incremental addition of first and secondpowder materials 54 and 56 to SFF structure 64. Build platform 58 iscapable of three dimensional (x,y,z) translation allowing threedimensional SFF features to be formed region by region as well as layerby layer. A translation direction of platform 58 is indicated by arrowt.

A benefit of SFF direct material deposition is that free standingcomponents can be formed with internal and external functionally gradedstructures to resist complex thermal mechanical induced internal stressfields during operation. Functional grading may be utilized to counterinternal property gradients in single material types such asmetal/metal, ceramic/ceramic, and CMC/CMC components in addition tometal/ceramic, metal/CMC, etc. composites. An example is shown in FIG. 4in which schematic turbine nozzle 70, comprises metal platforms 72 and74 and composite ceramic vane 76. In an embodiment, platforms 72 and 74are nickel based superalloys and vane 76 is a composite ceramicstructure with leading edge 76A and trailing edge 76B formed of twodifferent ceramic materials. Leading edge 76A is a first ceramic with alower CTE than trailing edge 76B which is a second ceramic. Duringoperation, the thinner trailing edge heats up and cools down faster thanthe thicker leading edge. As a result, trailing edge 76B is subjected tohigher longitudinal transient tensile and compressive stresses thanleading edge 76A as taught by commonly owned US2009/0028697 to Shi etal. and incorporated herein in entirety as reference. Functionallygraded regions 78 and 80 between metal platforms 72 and 74 and ceramicvane components 76A and 76B act to minimize internal stress due to CTEmismatch as discussed earlier. Functionally graded transition region 82between ceramic trailing edge 76A and ceramic leading edge 76B acts tominimize internal stress due to longitudinal strain mismatch resultingfrom CTE mismatch between the trailing and leading edge components ofcomposite vane 76.

It is to be understood that, while CTE is one property utilized in theinvention to minimize or eliminate internal stress concentrations, otherphysical, mechanical, optical, chemical and other properties known inthe art may be invoked in the SFF additive manufacturing fabrication offunctionally graded features of turbine components of the presentinvention. In particular, in addition to CTE, heat capacity, thermalconductivity and Young's modulus are properties contributing to internalstress generation and turbine components during service.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A monolithic composite turbine component may include: at least oneregion of a first material; a second region of a second material; and atleast one functionally graded transition region of the first materialand the second material between a first region and a second region.

The component of the preceding paragraph can optionally include,additionally and/or alternatively any, one or more of the followingfeatures, configurations and/or additional components:

A first material may be a metal;

A second material may be a ceramic or a ceramic matrix composite;

The component may be formed by a solid freeform (SFF) additivemanufacturing process;

The solid freeform (SFF) additive manufacturing process, may beselective laser melting (SLM);

The component may be a nozzle or a vane;

The component may be a rotating airfoil, bucket or blade;

The component may be a combustor panel, combustor heat shield, orcombustor fuel nozzle;

The metal may be selected from the group consisting of nickel base, ironbase, cobalt base superalloy, titanium and titanium alloy;

The ceramic may be selected from the group consisting of siliconcarbide, silicon nitride, silicon oxynitride and aluminum oxide;

The ceramic matrix composite may be selected from the group consistingof SiC/SiC, SiC and SiC/Si.

A method of forming a monolithic composite turbine component containingseparate regions of different materials may comprise: forming at leastone first region of a first material; forming a graded transition regionon the first region with composition of the transition region changingfrom a first material to a second material as the forming of thetransition region progresses; and forming a second region of a secondmaterial on the transition region.

The method of the preceding paragraph can optionally include,additionally and/or alternatively any, one or more of the followingfeatures, configurations and/or additional components:

The first material may be a metal;

The second material may be a ceramic or ceramic matrix composite;

Forming may comprise solid free form (SFF) additive manufacturing;

Additive manufacturing may comprise direct laser melting;

The metal may be selected from a group consisting of nickel base, ironbase, and cobalt base superalloy, titanium, and titanium alloys;

The ceramic may be selected from a group consisting of silicon carbide,silicon nitride, silicon oxynitride, and aluminum oxide;

The ceramic matrix composite may be selected from a group consisting ofSiC/SiC, C/SiC, and SiC/Si;

The component may be a nozzle, vane, rotating airfoil, bucket, blade,combustor panel, combustor heat shield or combustor fuel nozzle.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A monolithic composite turbine component comprising: at least onefirst region of a first material; at least one second region of a secondmaterial; and at least one functionally graded transition region of thefirst material and the second material between a first region and asecond region of the component
 2. The component of claim 1 wherein thefirst material is a metal.
 3. The component of claim 1 wherein thesecond material is a ceramic or a ceramic matrix composite.
 4. Thecomponent of claim 1 wherein the component is formed by a solid freeform(SFF) additive manufacturing process.
 5. The component of claim 4wherein the solid freeform (SFF) additive manufacturing process isselective laser melting (SLM).
 6. The component of claim 1 wherein thecomponent is a nozzle or a vane
 7. The component of claim 1 wherein thecomponent is a rotating airfoil, bucket, or blade.
 8. The component ofclaim 1 wherein the component is a combustor panel, combustor heatshield, or combustor fuel nozzle.
 9. The component of claim 2 whereinthe metal is selected from the group consisting of nickel base, ironbase, cobalt base superalloy, titanium, and titanium alloy.
 10. Thecomponent of claim 3 wherein the ceramic is selected from the groupconsisting of silicon carbide, silicon nitride, silicon oxynitride, andaluminum oxide.
 11. The component of claim 3 wherein the ceramic matrixcomposite is selected from the group consisting of SiC/SiC, C/SiC, andSiC/Si.
 12. A method of forming a monolithic composite turbine componentcontaining separate regions of different materials comprising: formingat least one first region of a first material; forming a gradedtransition region on the first region with composition of the transitionregion changing from a first material to a second material as theforming of the transition region progresses; and forming a second regionof a second material on the transition region.
 13. The method of claim12 wherein the first material is a metal.
 14. The method of claim 12wherein the second material is a ceramic or ceramic matrix composite.15. The method of claim 12 wherein forming comprises solid freeform(SFF) additive manufacturing.
 16. The method of claim 15 whereinadditive manufacturing comprises direct laser melting.
 17. The method ofclaim 13 where the metal is selected from a group consisting of nickelbase, iron base and cobalt base superalloy, titanium and titanium alloy.18. The method of claim 14 wherein the ceramic is selected from thegroup consisting of silicon carbide, silicon nitride, siliconoxynitride, and aluminum oxide.
 19. The method of claim 14 wherein theceramic matrix composite is selected from the group consisting ofSiC/SiC, C/SiC, and SiC/Si.
 20. The method of claim 12 wherein thecomponent is a nozzle, vane, rotating airfoil, bucket, blade, combustorpanel, combustor heat shield, or combustor fuel nozzle.